A weightlifter can benefit from the active involvement of a second person, commonly known as a spotter, during a weightlifting routine. This spotter serves two basic functions. The first is to prevent injury to the weightlifter. The second is to prolong the weightlifting exercise by providing aid to the weightlifter during the weightlifting repetitions. The second function allows the weightlifter to complete additional repetitions after his or her muscles have begun to fatigue. Completing repetitions with slightly fatigued muscles can help the weightlifter improve muscle stamina and increase muscle mass.
Many weightlifters face the drawback of not having skilled spotters to help them on a consistent basis. As a result, these weightlifters sometimes do not achieve the results they seek and grow disheartened with the sport. In response, weightlifting facilities staff trainers to whom all weightlifters have equal access. Unfortunately, it is impossible for only a few trainers to provide the services of a spotter to all these weightlifters at any one time.
In response to this drawback, inventors have designed user-controlled and microprocessor-controlled machines to serve both basic functions of a spotter. Most of these machines rely either on an electric motor to lift the weight or on a pneumatic device to vary the assistance to the exerciser, both in response to some form of an input from the exerciser.
A shortcoming of these machines is that they usually use cables. Unless the cables are continuously taut throughout the exercise, they can move suddenly, interfering with the exerciser's motion and causing discomfort.
Several of these machines also are not versatile enough to perform all the functions of a spotter. In particular, a machine that uses a motor to pull up a weight can not perform several certain functions of a spotter. A spotter can provide different amounts of assistance at different points in the exercise by applying different forces to the weight, while the exerciser applies the remainder of the force needed to counter gravity. Not until the very end of the exercise, if ever, does a spotter lift the weight out of the exerciser's hands. In theory, a motor can apply different forces as long as the voltage drop or the current across it can be varied. But in application, activating a motor turns a rotor, in turn (possibly through a transmission) lifting the weight on its own.
Machines with pneumatic devices unfortunately may require several seconds to vary the amount of assistance given to the exerciser, whereas a human spotter is able to provide the assistance immediately.